This week, a tweet went viral portraying a map of the worldwide range of the common rat.

As with all such maps, it shows a Planet Earth completely invaded by rats, save for polar regions and the territory within the pentagonal borders of Alberta.

“What … what happened in Alberta,” wrote British strength trainer Adam Fisher in the tweet, which has since been circulated nearly 5,000 times.

The rest of the world is frequently surprised to discover that in humanity’s centuries-long battle with the rat, there has been only one indisputable victor: The four million people of the Canadian province of Alberta.

“Norway rats are one of the most destructive creatures known to man,” reads the official Alberta government write-up on its world-renowned rat control program. “The people of Alberta are extremely fortunate not to have rats in the province.”

For nearly 70 years, Alberta has successfully kept rats from taking hold of an area larger than France — and it has done so by waging a vigilant and all-out war on the rodent.

“Rats are Coming!” a 1950s poster commissioned by the Government of Alberta.

Alberta Archives

“Because rat invasion is threatening Alberta, we need to be properly organized and know what to do, in order to fight the battle successfully,” reads a 1954 government booklet, Rat Control in Alberta, that was distributed with virtual ubiquity in the province’s public places.

Detail from the 1954 booklet Rat Control in Alberta.

Rat Control in Alberta

The booklet is eerily reminiscent of atomic civil defence guides published in the same era, and warned Albertans that if they failed to stop the rat, they faced an imminent future of destroyed crops, ruined pantries and even the bubonic plague.

“No person should spare any effort to kill every Norway rat he sees,” it adds.

Alberta was one of the last corners of North America to face the arrival of brown rats. The rodents had first set foot on the continent’s east coast around the time of the American Revolution, and had gradually been gnawing their way into the North American ever since.

Alberta government inspectors recorded the province’s first-ever sighting of rats in 1950 at a farm near the border town of Alsask, Saskatchewan.

Although the colony was quickly exterminated, a survey by the Department of Agriculture soon confirmed that it was merely the vanguard of more than 30 rat colonies discovered to have infiltrated the Alberta borderlands.

The rats had not yet penetrated any major settlements, and in a decision unprecedented in the history of rat-human relations, Alberta’s civil servants vowed that they never would.

Detail of an Alberta government map showing the Rat Control Zone in yellow.

Government of Alberta

The effort was organized very similar to a legitimate invasion. Teams of armed men were enlisted to man a newly designated “Rat Control Zone” along the Saskatchewan border. Behind the lines, meanwhile, civilians were trained in rat identification and extermination.

Public meetings taught citizens both urban and rural how to poison, trap and gas any suspected rats. Propaganda posters showed images vicious rats against the command to “kill.”

This war on the rats wasn’t optional: The province’s Agricultural Pests Act made it an offence for property owners not to immediately eradicate every rat they encountered. Enforcement of the law was largely unnecessary, however. A population of Albertans fresh off two foreign wars were eager to set their sights on invading rodentia.

You CanÂt Ignore the Rat!” 1950, a poster commissioned by the Government of Alberta.

Alberta Archives

The zeal of the effort was hinted at by the name of the go-to poison, provided free by the government: Warfarin.

While Alberta’s war on the rat lacks any cinematic adaptation, it has garnered a brief mention on Your Friend the Rat, a Pixar short that accompanied home video releases of Ratatouille. In it, animated Mounties are shown bravely fending off a rapacious tide of rats (some members of the rat patrol are indeed former Mounties).

“In 1950 rats invaded in the southeast border of Alberta, but were repelled by an impressive government rat control program,” says narrator Patton Oswalt.

So far, Alberta’s conquest of the rat is a feat that has been replicated only on the very smallest of scales.

The Atlantic island of South Georgia was declared free of rats earlier this year, but it took $17 million and more than 300 tonnes of airlifted poison bait over a period of 10 years.

Even then, South Georgia is one of the most remote places on earth, ensuring that it can easily quarantine itself against any rat comeback.

In this 2000 photo, Alberta Rat Control officers Orest Popil (left), Bruce Alexander (right) and Bill Kloeckes (middle) check out a farm field for rats near Kitscoty, Alberta. A stuffed rat sits on the hood of their truck.

Larry Wong/Edmonton Journal

But Alberta must constantly fend off new rat invasions from all sides. When Alberta calls itself rat-free, it’s referring to the fact that there are no breeding rats within the province. At any one time, a rat is standing on Alberta soil somewhere, but rat control exists to ensure that it will die quickly, and die childless.

Rat patrols continue to cruise the Saskatchewan border in a program. There is a hotline to report rat sightings: 310-RATS. Pet rats are strictly forbidden, with fines ranging in the thousands of dollars.Whenever rats appear in Alberta, it garners blanket news coverage for days on end.

Bylaw officer Todd Kabeya holds a dead rat found in the Auburn bay area of Calgary, Alberta, on August 17, 2012. A search was made of the area but there were no other rats found.

Mike Drew/Calgary Sun

Saskatchewan continues to be the main channel for invading rats, with the Rocky Mountains largely defending Alberta’s western edge. Nevertheless, the creatures are known to hitchhike on trucks, trains and even aircraft.

Two drowned rats found in Taber in 2011 prompted a statement from local authorities assuring the public that they had not been born locally. “It is likely the rats came off a train … and were quickly drowned when they hit the water,” said Taber bylaw officer Brandon Bullock.

In 2012, it was front page news in the Calgary Herald when a maintenance man found a suspected dead rat in one of the city’s apartment buildings. An investigation soon found that it was merely a squirrel.

Patty Robinson from Calgary Animal Services posing with a rat-like creature that turned out to be a squirrel.

Stuart Dryden/Calgary Sun

In one of the most major breaches of the Rat Control Zone in recent years, in 2012 a massive rat den was found dug into the Medicine Hat landfill. In an operation that took two months, rat controllers killed more than 150 individuals before declaring the area rat free.

“The problem is not solved,” warns the Alberta government website. “Rats have the capability to spread throughout Alberta just as easily today as they could in the past.”